Epstein-Barr virus (EBV) immunovirology was investigated as a marker for diagnosis/prognosis in (a) nasopharyngeal carcinoma (NPC) patients and (b) populations at risk for NPC. Specifically, the role of EBV virus capsid antigen (VCA) IgA antibody and EBV nuclear antigen (EBNA) was studied. In five normal individuals of Cantonese origin, a 10-fold increase of EBV-VCA/ IgA antibody over 1.5 years was diagnostic of NPC, and the presence of EBNA in the tumor cells correlated with the diagnosis. IgA antibody detected in tissues from the fossa of Rosenmueller identified NPC in 40 cases of so-called occult primary tumors of the head and neck. EBV serology correlated in a follow-up of 71 NPC patients since 1978. In general, NPC antibody titers were useful is a follow-up of undifferentiated (UC) and nonkeratinizing carcinomas (NKC-2) of the nasopharynx. Moreover, IgA titers were inversely related to ADCC titers in UC-NPC but not in non-NPC patients. Total B and T cell counts and skin testing provided good prognostic markers for patient follow-up. Depletion of IgA from UC-NPC patients sera removed the lymphocyte inhibition (LSI) activity. However, one such serum did exhibit a 40% inhibition of LSI, suggesting the presence of other inhibiting factors besides LSI. The presence of amyloid infiltration in 12% of NPC cases had never been reported previously. Herpesvirus saimiri (HVS) monoclonal antibodies were characterized as to their biological activity against two strains of HVS and herpesvirus ateles (HVA). Monoclonal antibodies were classified into 11 groups, as determined by immunofluorescence (IF) patterns in the nucleus or cytoplasm of cells. They failed to react with two strains of HVA or with HVS early antigen (EA)-producing cells. None of the antibodies neutralized HVS or HVA.